Pressure-limiting device



Aug. 9, 1960 J. L. GRATZMULLER PRESSURE-LIMITING DEVICE 2 Sheets-Sheet 1 Filed Feb. 19, 1957 IHIIII Ire/v 8122221 Gl atzmu 6 661' Aug. 9, 1960 Filed Feb. 19, 1957 J. L. GRATZMULLER PRESSURE-LIMITING DEVICE 2 Sheets-Sheet 2 Unit d States atentO PRESSURE-LIMHING DEVICE Jean Louis Gratzmulle r, 30 Ave. Georges Mandel,

l Paris 16c, France Filed Feb. 19, 1957, Ser. No. 641,113 Claims priority, application France Mar. 2, 1956 4 Claims. (Cl. 121-38) This invention relates to hydraulic systems in which a column of liquid is liable; to be entrapped during long periods byperfectly tight valve means in a portion of limited capacity of a hydraulic. circuit, so that several causes, and in particular the expansion of the liquid thus entrapped, may .give rise. to dangerous, or at least obj'ectionable, overpressures.

A simple illustration of such a system is the conventional hydraulic control including a jack and a three-position valve to put said jack into communication either with a source of pressure liquid or with a tank, or to tightly interrupt 'bothcommunications. In this last condition, a, column of liquid may be entrapped by the valve in the jack and its conduit.

An object. of the invention is to provide a device capable of limiting at any time the pressure in. a space in Which, a column of liquid is liable to be entrapped to a value equal to that of the. pressure in the source from which said liquid is supplied.

Another object of the inventionis to provide a pressure-limiting device of the type described, to be used in combination with a hydraulic system including a circuit hereinafter called a holding circuit capable of maintaining, in a utilization circuit, the hydraulic pressure of a source upon', actuation of a first push-button valve and as: long as evacuation is not triggered by a second pushbutton valve.

In, such a, hydraulic system, the holding function implies tightness of the said first push-button valve when the same is'not actuated. Now, in practice, such a tightnessis difficult to obtain, so that a non-return means must be interposed in theholding circuit to prevent return of liquid from'said' circuit towards said first push-button valve.

' On. the other hand, in. such a system, it is advantageous'to. ensure. a permanent sustaining of the pressure liquid in the holding circuit from the utilization circuit. Finally, to avoid an unwanted evacuation of liquid through the utilization circuit in case of a sudden drop-of pressure therein, anon-return valve opposing any flow of liquid from the holding circuit towards the utilization circuit must be interposed in the conduit provided to ensure the said sustaining, l Under these: conditions, the mass of hydraulic liquid contained in the holdingcircuit is completely entrapped ere Now, it is known that the volumetric expansion coefiicientof liquids, and in particular that of oil, is high as compared with their compressibility. Consequently, if a substantial temperature increase happens while the Holding device is operative, the pressure in the holding ci-r- {:uit may build up to a considerable value, liable to jeopardize the whole installation, or at least to render its sec et n m oss It is therefore a particular object of the invention to provide a by-pass between such a holding circuit and the source of pressure liquid, and'to incorporate in said byscribed; exhaust cireuit, while, establishing a feeding 2,913,262 Patente Au 9, 2.69

lice

. 2 pass a non-return means permitting flow of liquid only from said holding circuit towards. said source.

In this particular application, the use of such a unidirectional by-pass further oife'rs the advantage that, if the pressure in the source becomes insufficient for the purpose aimed at, the holding pressure-also drops, which causes immediate, evacuation, of liquid from the holding circuit and, hence, closing. of the admission valve of the utilization circuit. Furthermore, when the normal pressure of the source is resumed, the abovermentioned non-return means prevents any unwanted reopening of the admission valve from taking. place, said opening being only possible anew when the first push-button valve is actuated again. There is thus provided; a simple solution to the known problem consisting, when the execution of an. order can not be completed due to a failure of the source of power, in prohibiting any unexpected furtherance'of the said execution when the cause of said failurehas been elimi: nated.

Gther objects and advantages of the invention will be hereinafter described with reference to the accompanying drawings, given. merely by way of example.

In these drawings:

Figure ll is .a diagrammatic view of a hydraulic system with a holding circuit provided with a pressure-limiting device according to the invention.

7 FigureZ is a. general layout of an installation adapted to the hydraulic control of a. circuit-breaker and comprising a hydraulic device for holding the same in its cir, u t-m k n r it en- In the diagram of Figure .1 is shown at 1 a source, of pressure liquid constituted; by. a hydraulic power accumulator, a main feeding conduit 2 connecting the source, 1 with a selector valve 3 which further communicates through a duct 4with a tank 5 and through parallel ducts 6 and;7 with a single conduit 8 used for feeding as well; as for exhausting a hydraulic motor constituted by a single..- acting hydraulic jack comprising a cylinder 9, a piston 0 and r turn p i g In the exhaust position shown, the sliding member 12 of the selector valve 3. sets thepipes 8 and 7 connected with the jack 9 into communication with the exhaust duct 4 'In th sv sameposition, the sliding valve member 12 interrupts, any communication between 'the conduit 2- and the'ducts 6 and 8 connected to the jack 9.

Conversely, in its adrnission position (not shown) the sliding valve member 12 interrupts the above-de cuit between the source land the jack 9, through cond t ndlil fia The sliding valve member 1 2 i s rigid with thepiston rod A 13,of an-auxiliary jack comprising a cylinder 14, a piston 15,'and1 a returnspring 'ldwhich, when jack 14 is corn nectedwith tank 5, brings the" movable assembly 15 inthe exhaust. position shown inthe figure and holdsit there, Conversely, when the jack114i is put under pressure, thejpistoii rsfbri gs the movable 15,?131'12 into. admission position against the action of spring 1.15: There; ng of the] auxiliary acking ensured byjt 5 parallel ..circuits.f'..'ljhe,'niain feedingfcircuit of the jacli 14 comprises -a ,pipej 17 connecting the source 1 withing chamber ofa pilot slide valve 18 controlled. bya push;- botton 18a urged towards its rest positipnin which pipe 17, is, sealed on bye; return spring 18b, and al ductlll, interconnecting'the said iclia'mber with the jack 14: A, second, holding circuit comprises a conduit 20 lea f fromthe duct}, towards the jack 14 and-in which incorporated "a non-return valve 21 preventing, liq d fl vrfrcm the ia s 1A. owardsthedmtfi. and 'affl strictorj22, bet en the nonreturn. hal e ,1

The evacuation of liquid from 'the 'jack 'l'd' via the duct 19 is 'eifected through an evacuation branch pipe 18 opens and puts the auxiliary jack 14 into cornmunim cation with the source 1 through the pipes 17 and 19. The auxiliary jack 14 is' thus put under pressure and displaces the sliding valve member 12 from the exhaust position as shown, to the admission position in which the source 1 is put into communication with the jack 9, I

as described above. As soon as the push-button 18a is released, the slide valve 18 interrupts the communication between the auxiliary jack 14 and the source 1; the jack 14, howevercontinues to be fed from duct 8 through the holding circuit 20; consequently, the auxiliary jack 14 remains under pressure and the sliding valve member 12 is kept in its admission position. v p These conditions persist until an action, exertedon the push-button 25, establishes an exacuation communication between the jack 14 and the tank through the pipes 19, 23 and duct 4, which are so dimensioned that'the rate of flow through them is higher than the rate of flow through the pipe, as 20 limited by the flow restrictor 22, so that the jack 14 is emptied and its return spring 16 brings the sliding valve member 12 into the exhaust position shown. The main jack 9 is then emptied in turn and the liquid previously contained therein flows towards the tank 5 through the pipes 8, 7 and 4.

In the above-described device, it may be seen that, except during the periods in which the valves 18and 24 are open, the column of liquid contained in the circuit portion comprising the working chamber of the jack 14, the section of the duct 20 extending between the jack 14 and the non-return valve 21, the pipe 19 and the section of the branch 23 which extends between the pipe 19 and the slide valve 24, is trapped between the slide valve 24 and the non-return valve 21. Under these conditions, any increase of the ambient temperature, such as would otherwise cause a volumetric expansion of the liquid column so trapped would give rise to an increase of pressure therein.

According to the invention, in order to prevent the pressure in the trapped liquid column from building up to a value higherthan that of the source 1, there is provided between the circuit portion in which the liquid is trapp d and the source, a by-pass 27 in which is incorporated a non-return valve 28 which permits liquid to escape from the trapped column towards the source, while preventing flow from the latter towards the holding circuit.

Independently of this principal function, the non-return valve 28 has other functions.

In particular, as clearly shown in Figure 1, if at any time the pressure of the source 1 becomes insufficient to hold the piston of the jack 9 in operated position against the action of the return spring 11, the holding pressure, which is limited to that of the source, owing to the presence of the non-return valve, will become insufficient itself to hold the auxiliary jack 14 actuated (both jacks and their springs beingv suitably calibrated to this effect). Under these conditions the sliding valve 12 Will be brought back into the exhaust position and the jack 9 will rapidly return to its unenergized position.

Moreover, subsequently to such a failure, once the same has been eliminated, the presence of the non-return *valve 28 prevents any unwanted automatic build-up of the pressure in the jack 9 by prohibiting any feeding of the holding circuit as long as the sliding valve 18 is not :re-opened.

' Figure 2 shows a complete embodiment of a hydraulic control system according to the invention, to be asspciated with a circuit-breaker.

This system comprises essential parts generally designated in Figure 2 by the same reference characters as in Figure 1. These essential parts include an air-and-oil accumulator 1, a circuit-making pilot valve 18 corresponding to the slide valve 18 of Figure l and a circuit-breaking pilot valve 24 corresponding to the slide valve 24 of Figure 1.

In this installation, there is also provided a self-evacuating device for the accumulator 1, generally shown at 30, of the general type described in the application Serial No. 606,482, filed August 27, 1956, and a quick evacuating device, generally shown at 31, of the general type described in the application Serial No. 474,538, filed December 10, 1954, now Patent No. 2,888,909 granted June 2, 1959.

The presence of the self-actuating device 30 of the accumulator it ensures better conditions of resetting to resting state of the installation when the pressure in the source 1 happens to drop. As described in the first above-cited application, this device comprises a normally closed valve for draining the oil compartment 32 of the accumulator 1. The drain valve has a push member which normally extends a certain distance into the com partment 32. When the holding circuit is full of 'oil the movable partition of accumulator 1 does not reach,

the push member of the drain valve, but when, owing, for example, to loss of oil from the holding circuit, the movable partition of the accumulator rises to near the cylinder head of the accumulator, it engages the push member and pushes it upwards to open the drain valve, the extension of the push member into the compartment 32 being sufiicient to ensure that when the movable partie tion of the accumulator meets the cylinder head, the valve is full open.

If, from this instant when the piston comes into contact with the push member of the drain valve, the quantity of oil contained in the compartment 32 and in the holding circuit diminishes, even very slightly, for any accidental reason whatsoever, such as leakage, in continuing its stroke, the movable partition of accumulator 1 will actuate the drain valve and bring the compartment 32 into communication wtih the drain passage 35, which brings about the complete and rapid drainage of the rest of the compartment 32 and of the holding circuit.

Once draining is initiated the accumulator 1 is rendered completely inoperative. In order to enable it to be brought back into operation, there is provided a priming device including a normally open valve which can be closed temporarily by means of a hand actuated lever, to interrupt communication between the drain valve and the drain passage 35.

On the other hand, the presence of the quick discharge device 31 has for its effect to reduce the duration of the evacuation of liquid from the auxiliary valve 14 and hence, the time of response of the main jack to the circuit-breaking order.

In this installation, the combination of the non-return valve 28 with the self-evacuating device 30 and the nonreturn valve 21, has the following eifects:

(a) The push-button 18a need be actuated onlyduring the time strictly required by the piston15 to complete its stroke; this action may even be interrupted be fore the pressure has fully built up in the pipe 8. Thisis due to the fact that the liquid entrapped in the holding circuit portion between the non-return valve 21 and the pilot valve 18 is prevented from escaping owing to the presence of the valve 21.

(b) If owing to a sudden increase of temperature,- the liquid contained in the above-mentioned circuit portion expands, the excess liquid can escape towards the source 1 through the non-return valve 28.

(c) When the stock of liquid in the accumulator 1 is insuflicient, the pipe 8 leading to jack 9 and the source are emptied by the self-evacuating device.30 and the holding circuit portion above mentioned is also emptied owing to the presence ofthe non-return valve 28; thus, the main valve 12 comes back into its resting position under the action of the spring 16, and when a normal pressure is reestablished in the source 1, the pipe 8 is not fed again.

In a general manner while, in the above description, is disclosed what is deemed to be practical and efficient embodiments of the invention, it should be well understood that it is not wished to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention.

What is claimed is:

l. A hydraulic system for selectively feeding a hydraulic circuit with liquid from a source of pressure liquid and thereafter limiting at any time the pressure in said circuit at a value at most equal to the instantaneous pressure at the outlet of said source, said system comprising a feeding duct connecting said source with a portion of said circuit, valve means to selectively open said duct until said circuit portion is filled with liquid and then to tightly re-close said duct, 21 by-pass to connect said circuit portion with said source without passing through said valve means and a non-return means interposed in said by-pass to permit free flow of liquid from said circuit portion towards said source whenever the pressure in said circuit portion is higher than that at the outlet of said source While tightly preventing at any time flow of liquid from said source towards said circuit through said by-pass.

2. -A hydraulic system according to claim 1, further comprising selectively operable valve means to evacuate liquid from said circuit.

3. A hydraulic system for selectively feeding a hydraulic circuit with liquid from a source of pressure liquid upon actuation of a tight push-button valve and thereafter maintaining in said circuit a pressure at most equal to that of said source until operation of evacuation means, said system comprising a three-way valve means separately connected with said source, with said circuit and with an evacuation tank, said valve means having a resting position in which it establishes a communication between said circuit and said tank while isolating said source and an operative position in which it establishes a communication between said source and said circuit while isolating said tank, a hydraulic jack connected with said valve means to bring and hold the same in said operative position, means to feed said hydraulic jack with liquid from said source in response to actuation of said pushbutton valve, means to permanently communicate said circuit with said jack to maintain liquid pressure therein as long as said circuit contains pressure liquid, said evac nation means being operable to connect said jack with said tank and thereby return said three-way valve means into said resting position, a non-return means to prevent flow of liquid from said jack into said circuit, bypass means to communicate said jack with said source Without passing through said tight push-button valve and a non-return means to prevent flow of liquid from said source into said jack through said by-pass means.

4. In a hydraulic system for controlling the feeding and exhausting of a single acting hydraulic motor through a combined feed and exhaust duct selectively connectible to a hydraulic pressure source and to exhaust by a main selector valve actuated by a hydraulic relay, a pilot valve operable to initiate excitation of the hydraulic relay to connect said feed and exhaust duct to said pressure source, a holding circuit connecting said feed and exhaust duct to said relay for maintaining the excitation of said relay after closure of said pilot valve, a non-return valve in said holding circuit preventing feed-back from said relay to said feed and exhaust duct, a by-pass from said holding circuit to said pressure source, and a second non-re turn valve preventing flow from said pressure source towards said holding circuit.

References Cited in the file of this patent UNITED STATES PATENTS 1,944,351 Landry Jan. 23, 1934 2,397,299 Strid Mar. 26, 1946 2,467,508 Trautman Apr. 19, 1949 2,660,984 Zumwalt Dec. 1, 1953 

